Heat-resisting structure, etc.



Patented Mar. 5, 1929.

- UNITED STATES Nam vrc'ron mmnrrn, or wrmameron, nsnawmn;

HEAT-BESISTING STRUCTURE, ETC.

no Drawing. a lication ,flled May This invention relatesto improvements in i the production of heat-resisting alloys adapted to'withstand'high temperatures.

The heat-resisting'alloys made according to the present invention are valuable for making castings and otl1er",structures, such as heat treating or malleabllzmg boxes, heat-resisting cylinders and apparatus for the chemical industries where a temperature of around .1150

C. is to be maintained for long periods of time and under oxidizin g or reducing tonditions.

The new alloys are made of'nickel, chromium' and iron and preferably with small amounts of deoxidizing a I minum, magnesium, etc. Xlloys have heretofore been made of nickel, chromium and iron for heat-resisting structures, but these alloys n so have contained an increased amount of nickel or ofchromium, or both, or have otherwise been of different composltion from the new alloys. The new alloys can be produced at a greatly reduced cost as compared with heatresisting alloys heretofore manufactured, while they nevertheless possess the desirable properties of withstanding high temperatures.

for long periods of time.

I have found that a very satisfactory heatresisting alloy can be made containing only about 10% chromium with about 30% nickel and nearly of iron. These percentages are capable of some variation, but my investigations indicate that the chromium should be at least 8% and the nickel at least 28%, since, below these percentages, a considerable change in the properties of the alloys appears to take place. The chromium may be as high as 15%, but there appears to be little advantage in increasing it above 12%. An increased amount of nickel, about 30%, can be used, for example, up to as much as of nickel, and with corresponding reduction in iron, but I have found that such a large percentage of nickel is not necessary, and increase in nickel increases the cost of the alloy.

I have found that it is advantageous to reduce the chromium content to practically the lowest possible amount, since, by doing so, it is possible to do away with the use of the electric furnace, and to produce the alloys and resmelt the scrap in an ordinary openhearth furnace. This enables the alloys to be produced at decreased expense and to be more easily manipulated.

I have further found that by reducing the chromium to the amount indicated, this chromium can be supplied in the form of ordinary ents such as a'lu 1922, smart 36.558364.-

ferro-chromi um which is much less expensive than the high grade low-carbon chromium and chromium alloys heretofore used in makmg high chromium nickel alloys. I have also found'that' the new low chromium alloys have a high scrap value, and that the scrap can be.

resmelted in-an ordinary reverbratory furnace without excessive loss of chromium or nickel; while .any' loss of chromium can be readlly made up by addition of ordinary ferro-chromium to the charge or bath. The

newalloys can accordingly be re-smelted at a minimum cost.

For the production of'good castings that will withstand high temperatures it is necessary that the castings should be malleable at about 1100 0., since otherwise they will tend to crack. If they are malleable at ordinary temperatures, they will tend to become too soft and lose their shape at temperatures around 1100 C. unless the chromium content is very high. In order to produce satisfactory castings which are malleable at high tem peratures without being too soft, it is .important to have a proper carbon content of the alloys, when the'alloys contain only about 10% of chromium. In so far as I am aware,

the importance of a proper carbon content in low, for example, as low as 0.25%, the alloy becomes malleable at ordinary temperatures and is less advantageous for castings intended for use at-high temperatures. If the carbon content is around 1% or higher there is danger of cracking. Accordingly, in making the new heat-resisting alloys for use in castings which are intended to withstand high temperatures, I keep the carbon content around 0.5% to 0.75%. The use of much larger amounts of carbon, for example, around 2% in chromiumnickel-iron castings, lowers the melting point of the alloy and substantially destroys its mallcability at high temperatures.

Where, instead of castings for use at high temperature, the alloys are to be used for purposes where malleability at ordinary temperatures is desired, a lower carbon content is advantageous. If, for example, the carbon is reduced below 0.4% and if a sufiicient amount of deoxidizing agents are added (e. g. 1 to 2% of manganese) the alloy becomes so malleable that it can be rolled, hammered and drawn into sheets and wire, which are heatresistin at temperatures around 1150 C. Such a1 oys are valuable for man purposes such as heat-interchangers for preeating air by the use of flue ases or productsof combustion, for walls 0 annealing boxes and carbonizing boxes, and to some extent for electric heating wires, although the alloys'do not possess the same qualities in electrical resistance as alloys with higher chromium content.

The new alloys, as previously stated, have a comparatively high scrap value. The scrap can be smelted down in an ordinary open-.-

hearth furnace with an oxidizing atmosphere and with a loss of only about 20% of the chromium, 9.5% of the nickel, and 6% of the iron in the slag. For example, with an alloy containing 10% chromium, 30% nickel and nearly 60% iron, only about 2% chromium would be lost in the slag and about 8% will remain in the alloy. The necessary addition of chromium, can be made in the form of high-carbon ferro-chromium without introducing an objectionable amount of carbon into the alloy. The slag produced in the re-smelting operation has a composition, for example, of 20% chromium, 4% nickel and 25% iron. The chromium loss on re-smelting, accordingly, is

not excessive and can readily be made up by the cheapest commercial grade of ferro-chromium. V

In the manufacture of the alloy, ordinary ferro-chromium can similarly be used. If the amount of carbon introduced with the ferroii chromium, together with that present in the iron or steel used, is too high, this can be reduced by leaving the bath in the open-hearth furnace, or the carbon can be reduced in the iron or steel bath before the ferro-chromium is added, or an oxidized bath can be used which will assist in oxidizing and removing a part of the carbon. On re-smelting the scrap, I have found that a reduction in carbon takes place which is somewhat larger in proportion than the loss of chromium, so that the addition of high-carbon ferro-chromium to make 111p the loss of chromium will introduce about t e right amount of carbon into the alloy, pgrticularly in the case of allo s where a car-- 11 content of around 0.5 to 0.; 5% is desired.

While I do not-desire to limit myself by any theoretical explanation of the part which the different ingredients contribute to the alloys, my-theory is that the chromium is necessary to produce a coating of oxides which is 1m rvious to the surrounding atmosphere,

which will not reduce in contact with carbon, and will not react with the-metal underneath; and that thechromium also gives to the alloy an amount of hardness so that it will retain its shape without bending atthe temperature at which it is used. The nickel seems to produce or assist in producing a non-scaling oxide film and to keep the alloy from'crystallizing. The iron, although it is partly a dilutinglagent for the nickel and chromium, nevert ele'ss seems also to have a certain beneficial mfiuence, since I have found, for example, that with alloys containing a lower content of chromium (about 5%) the alloy is heat-resistin when made with 80% nickel and 15% iron gas described in my co-pending application, erial No. 558,7 while it is not heatresisting to the same degree when it was made with 95% nickel and no iron. I conclude, therefore, that the iron'has some other influence than merely as a diluting agent in the new allo s of the present invention.

In so ar as I am aware, no systemmatic investigation has been made to determine the best proportions for producing a satisfactory heat-resisting alloy, possessing the necessary qualities, at a minimum expense of manufacalloys have contained a much higher content of chromium and usually a higher content of nickel. My investigations have indicated that the lowest permissible chromium content depends upon the amount of nickel that is present, and vice versa. The use of the pro er amount of nickel with substantially t e minimum amount of chromium, for example, around 10% of chromium and 30% of nickel, enables the alloy to be produced at greatly decreased expense and to be re-smelted in a more advantageous way. That is, the addition of the proper amount of nickel makes itpossible to reduce the chromium content to within the limits for satisfactory open-hearth furnace work, and the scrap has a considerably increased value as compared with alloys which are higher in chromium and lower in iron, where the scra value is less because of the slag loss and t e expense of re-s'melting in electric furnaces.

In so far as I am aware, it has not heretofore been considered possible to make a satisfactory high temperature heat-resisting al loy containing less than 12% of chromium, I have discovered, however, that such an al loy can advantageously be made byproper adjustment of the other ingredients. Instead of a higher chromium content being the criterion of better quality, I have demonstrated that excellent resultscan be obtained if there is a proper relation between the nickel, chromium and carbon. Where the chromium content is considerably higher, for, example, around 20%, a greatly reduced carbon content is necessary, e. g. around 0.2%; but with a low chromium content around 10%, a much higher carbon content, but one which is not too high, is necessary for best results in the will be evident from the For castings intended to withstand high temperatures, the carbon content should not be over 1% and should not be less than 0.30%, and for best results it should be about 0.5 to For alloys which are malleable at. ordinary temperatures, a lower carbon content is permissible.

The advantages of the resent invention act that the new alloys can be made at practically one-half the cost of alloys heretofore manufactured with a higher chromium content and with a low carbon content around 0.20 to 0.25%. As compared With such higher chromium alloys, the new alloys can be made of ordinary ferrochromium instead of the more expensive lowcarbon chromium required in high chromium 4 alloys.

The new alloys can also be made more advantageously and at less cost in an ordinary reverberatory furnace than in an electric furnace such as has heretofore been commonly used in the ma ufacture of heatresisting alloys. The new lloys also have an increased scrap value and. can be re-smelted more advantageously and with less loss and expense than high chromium alloys.

In the manufacture of the new alloys 3 have found it advantageous to make use of manganese, aluminum and magnesium as deoxidizing agents; and I have found it particularly advantageous to use small amounts I of all three of these agents together. Some small amount of manganese may be present in thefinal alloy, but the amounts of aluminum and magnesium used will be so small that only traces at most will be present in the final alloy. The amount of manganese may thus be from- 0.5% to 5% and varyin amounts may remain in the final alloy an mziy be advantageous therein.

. claim;

1. The method of producing chromiumnickel-iron alloys which comprises smelting together chromium, nickel and iron in the proportions of about -15% chromium, nickeland 50-60% iron in an openhearth reverberatory furnace, and regulating the carbon content of the alloy so that it will contain about 050-0.? 5% carbon.

2. The method of re-smelting scrap alloy containing about 10-15% chromium, 30-35% nickel, and 5060% iron, which comprises smelting the same in an o en-hearth reverberatory furnace and supp ying added chromium in the form of ferro-chromium.

3. The method of producing chromiumnickel-iron alloys which comprises smelting together iron and nickel in a reverberator furnace inan oxidizing atmosphere, and a ding high-carbon ferro-chromium to the bath with resulting reduction of the carbon content of the alloyby oxidation.

In testimony whereof I afiix my signature.

' NOAK VICTOR HYBINETTE. 

